title: p16(INK4a) protects against dysfunctional telomere-induced ATR-dependent DNA damage responses.
abstract: Dysfunctional telomeres limit cellular proliferative capacity by activating the p53-p21- and p16(INK4a)-Rb-dependent DNA damage responses (DDRs). The p16(INK4a) tumor suppressor accumulates in aging tissues, is a biomarker for cellular senescence, and limits stem cell function in vivo. While the activation of a p53-dependent DDR by dysfunctional telomeres has been well documented in human cells and mouse models, the role for p16(INK4a) in response to telomere dysfunction remains unclear. Here, we generated protection of telomeres 1b p16-/- mice (Pot1bΔ/Δ;p16-/-) to address the function of p16(INK4a) in the setting of telomere dysfunction in vivo. We found that deletion of p16(INK4a) accelerated organ impairment and observed functional defects in highly proliferative organs, including the hematopoietic system, small intestine, and testes. Pot1bΔ/Δ;p16-/- hematopoietic cells exhibited increased telomere loss, increased chromosomal fusions, and telomere replication defects. p16(INK4a) deletion enhanced the activation of the ATR-dependent DDR in Pot1bΔ/Δ hematopoietic cells, leading to p53 stabilization, increased p21-dependent cell cycle arrest, and elevated p53-dependent apoptosis. In contrast to p16(INK4a), deletion of p21 did not activate ATR, rescued proliferative defects in Pot1bΔ/Δ hematopoietic cells, and significantly increased organismal lifespan. Our results provide experimental evidence that p16(INK4a) exerts protective functions in proliferative cells bearing dysfunctional telomeres.
authors.forename: Yang
authors.initials: Y
authors.lastname: Wang
authors.forename: Norman
authors.initials: N
authors.lastname: Sharpless
authors.forename: Sandy
authors.initials: S
authors.lastname: Chang
mesh_terms: D000375:Aging; D000818:Animals; D017209:Apoptosis; D064007:Ataxia Telangiectasia Mutated Proteins / Q000378:metabolism; D016026:Bone Marrow Transplantation; D049109:Cell Proliferation; D002478:Cells, Cultured; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000502:physiology*; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000378:metabolism; D004249:DNA Damage; D004260:DNA Repair; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D005260:Female; D006410:Hematopoiesis; D006412:Hematopoietic Stem Cells / Q000502:physiology; D007421:Intestine, Small / Q000473:pathology; D008297:Male; D051379:Mice; D016513:Mice, SCID; D008822:Mice, Transgenic; D055550:Protein Stability; D017384:Sequence Deletion; D013154:Spleen / Q000473:pathology; D016615:Telomere / Q000502:physiology*; D059505:Telomere Homeostasis; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism
chemical_list: C417743:Cdkn2a protein, mouse; D019941:Cyclin-Dependent Kinase Inhibitor p16; D050759:Cyclin-Dependent Kinase Inhibitor p21; D004268:DNA-Binding Proteins; C512707:POT1b protein, mouse; D016159:Tumor Suppressor Protein p53; C576897:Atr protein, mouse; D064007:Ataxia Telangiectasia Mutated Proteins